Generally, a front panel of a car chamber within a vehicle is attached with side hinge pillars or A pillars onto the left and right sides thereof, and a tie bar shaped as a pipe is transversely installed across the side hinge pillars provided on both sides. An instrument panel which is fixed to the tie bar is equipped with various adjusting devices of the vehicle such as a speedometer and an audio system and an air bag for protecting passengers.
Meanwhile, when a car crash is taking place, a submarine phenomena occurs such that the lower part of the body of a driver or a passenger occupying an assistant driver's seat is forcibly pushed down to be put under the instrument panel due to the inertia. In this case, the knee of the driver or the passenger sitting on the assistant driver's seat is run into the framework of the vehicle and, furthermore, the upper parts of the bodies of the passengers are inclined to move forward to the bottom side due to the submarine phenomena. Thus, even though the air bag is properly inflated upon the car crash, the upper part of the body hits against the lower side of the air bag or is to be out of the protecting coverage of the air bag. Thus, the air bag is detrimental to effective protection for passengers.
Therefore, a knee bolster is installed to the front of the instrument panel for absorbing the impact upon the driver or passenger occupying the assistant driver's seat during the car crash, so that the impact upon the knee of the passengers is decreased while preventing or reducing the inadvertent influence of the submarine phenomena.
The knee bolster is largely classified into two kinds: one for driver's seat and the other for assistant driver's seat. Here, since an interior package in front of the driver's seat has a different structure from that in front of the assistant driver's seat, the knee bolsters for driver's seat and for assistant driver's seat have different structures.
Typically, the knee bolster is fabricated by a plurality of pieces of steel plate to be coupled with one another via bolts or a welding to involve a lot of working processes, which degrades workability and productivity. In addition to this drawback, the number of the parts constituting the knee bolster is so many to make the part management difficult and dimensional stability be low because of a welding deformation, which, in turn, degrade the workability and assembling productivity.
Also, a substance of the conventional knee bolster is a steel to have a disadvantage of being too heavy, thereby increasing overall weight of the vehicle.
A conventional knee bolster is filled with a foam substance into a hollowed internal space, which also is heavy and so expensive.
FIG. 8 is a sectional view showing a general knee bolster 110 for assistant driver's seat. Knee bolster 110 is installed to an instrument panel (not shown) in front of the assistant driver's seat of an automobile to be integrally formed with a glove box 112 in a body. As shown in FIG. 8, knee bolster 110 includes an outer plate 114, an inner plate 116 and a shock absorbing plate 118 installed between outer plate 114 and inner plate 116. The shock absorbing plate 118 is formed of a steel.
In the conventional knee bolster formed as above, when the passenger collides against outer plate 114 of the knee bolster resulting from a car crash, the impact force caused by the collision is transferred to shock absorbing plate 118. If the impact force is slight, the stiffness of shock absorbing plate 118 elastically bears the impact force. Whereas, shock absorbing plate 118 is plastic-deformed by a strong impact force to absorb and eliminate the impact force.
In conventional knee bolster 110 described as above, however, the impact force is absorbed only by shock absorbing plate 118 formed of steel. Accordingly, the submarine phenomena cannot be prevented when the impact force is significantly powerful to be out of the confines of the deformation. What's worse, since shock absorbing plate 118 is formed of the steel, the impact applied to the passenger resulting from shock absorbing plate 118 is notably great as much, as a consequence, it has a drawback of involving a danger that the passenger is highly liable to be injured.
U.S. Pat. Nos. 4,662,649, 4,834,422, 5,071,162 and 5,312,133 disclose knee bolsters for automobiles which are related prior arts. Among these, U.S. Pat. No. 5,071,162 issued to Takagawa dated in Dec. 10, 1992 describes a knee bolster 120 for assistant driver's seat, in which an impact volume in the car crash is doubly absorbed by both a steel plate 128 and a urethane member 121. Knee bolster 120, as shown in FIG. 9, is provided with a steel plate 128 between an outer plate 124 and an inner plate 126 and a reinforcing plate 123 attached with a urethane member 121 onto the inner surface thereof. Inner plate 126 and reinforcing plate 123 are spaced apart from each other by an interval of .delta.. A reference number I denotes an instrument panel.
In the event of the car crash, the knee of the passenger presses outer plate 124 of knee bolster 120, and steel plate 128 primarily tolerates the impact force while being inwardly plastic-deformed. After steel plate 128 contacts reinforcing plate 123, reinforcing plate 123 secondarily absorbs the impact force.
However, above-described knee bolster 120 requires separate reinforcing plate 123, and it is very difficult to mold the urethane corresponding to the shape of reinforcing plate 123. Moreover, since inner plate 126 and reinforcing plate 123 are spaced apart from each other by the interval of .delta. the shock absorbing effect by urethane member 121 is relatively slight. Furthermore, urethane member 121 is adhered to reinforcing plate 123 which is then supported by a support member 125 without being additionally supported. For this construction, urethane member 121 cannot effectively afford a reaction force with respect to a passenger who imposes the impact force. Consequently, it can be noted that the shock absorbing effect by urethane member 121 is trivial.
In addition, support member 125 has a complicated structure and supports merely a portion of reinforcing plate 123. Thus, the reaction force afforded by reinforcing plate 123 is relatively weak.